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Regular version of the site

Article

A pointwise selection principle for maps of several variables via the total joint variation

Journal of Mathematical Analysis and Applications. 2013. Vol. 402. No. 2. P. 648-659.
Vyacheslav V. Chistyakov, Tretyachenko Y. V.

Given a rectangle in the real Euclidean n-dimensional space and two maps f and g defined on it and taking values in a metric semigroup, we introduce the notion of the total joint variation TV(f , g) of these maps. This extends similar notions considered by Hildebrandt (1963) [17], Leonov (1998) [18], Chistyakov (2003, 2005) [5,8] and the authors (2010). We prove the following irregular pointwise selection principle in terms of the total joint variation: if a sequence of maps {fj}∞ j=1 from the rectangle into a metric semigroup is pointwise precompact and lim supj,k→∞ TV(fj, fk) is finite, then it admits a pointwise convergent subsequence (whose limit may be a highly irregular, e.g., everywhere discontinuous, map). This result generalizes some recent pointwise selection principles for real functions and maps of several real variables.